This application claims priority to German Patent Application No. 10120432.9-12 filed Apr. 26, 2001, which application is herein expressly incorporated by reference.
The invention relates to a centered double universal joint, especially for driving, or for drives in, agricultural implements and tractors.
U.S. Pat. No. 3,470,712 describes a centered double universal joint. Two outer joint yokes are each articulatably connected via a cross member to two inner joint yokes. Each inner joint yoke is provided with a bearing housing portion. The bearing housing portions are bolted to one another. The bearing housing portions delimit an annular guiding recess which radially displaceably supports a guiding disc. Floatingly arranged annular guiding plates are provided between both sides of the guiding plates and the inner joint yokes in the guiding recess. The guiding disc has a centrally arranged guiding projection which, on both sides, projects from the guiding disc. A bore starts from each end face of the guiding projection. The bore is initially cylindrical and then hollow-spherical. The outer joint yoke arms of each outer joint yoke are connected to one another by a welded-in bridge. Each bridge has a journal projection with a spherical face that engages the associated bearing bore of the guiding projection of the guiding disc. At high torque values and large articulation angles, this design leads to a concentrated load. Thus, the concentrated load leads to an increase in wear in the region of contact between the spherical journal, associated with the bridge, and the respective cylindrical bearing bore which is engaged by the spherical journal. The purpose of the above-described centring means is to control the connected universal joints onto half the articulation angle between an input shaft and an output shaft in order to achieve constant velocity. If wear leads to play, the relationship is disturbed.
It is an object of the present invention to provide a centered double universal joint which ensures accurate control of the universal joints that form the double universal joint onto half the articulation angle. This achieves a long service life.
In accordance with the invention, a centered double universal joint comprises: A first outer joint yoke has first yoke arms and a first bridge that connects the two first yoke arms. The first bridge carries a first cylindrical bearing journal. A first inner joint yoke includes a first bearing housing portion. A first cross member articulatably connects the first outer joint yoke to the first inner joint yoke. A second outer joint yoke has second yoke arms and a second bridge that connects the two second yoke arms. The second bridge carries a second cylindrical bearing journal. A second inner joint yoke includes a second bearing housing portion. The second bearing housing portion is connected to the first bearing housing portion and forms an annular guiding recess. A second cross member articulatably connects the second outer joint yoke to the second inner joint yoke. A guiding disc has a central guiding projection which projects on both sides of the guiding disc towards the first and the second bearing journal. The guiding projection has a continuous cylindrical bearing bore. The two bearing journals extend into the bearing bore from different ends. The guiding disc is adjustable in the guiding recess. A bearing ball is on each bearing journal. The bearing ball has the shape of an outer spherical zone and has a through-bore. The through-bore enables the bearing ball to be positioned on the bearing journal. The bearing ball is held at least axially with reference to the axis of the bearing journal. The bearing ball has a spherical outer face. A bearing race for each bearing ball is supported in the cylindrical bearing bore. The bearing race supports the spherical outer face of the bearing ball. The bearing race includes a corresponding hollow spherical bore that enables the bearing ball to pivot in all directions. The bearing race and the bearing ball form a preassembled unit. The bearing race has a cylindrical outer face which is adjustably positioned in the cylindrical bearing bore of the guiding disc.
An advantage of this design is that a lower surface pressure and, in consequence, greatly reduced wear is achieved between the guiding disc bearing bore and the bearing race, on the one hand, and between the bearing race and the bearing ball, on the other hand. This is achieved by a surface to surface contact between the conforming surfaces. In addition, it is possible to provide at least one of the components with a friction-reducing coating or to produce it from a material with advantageous friction value. The bearing ball and the bearing race can be pre-assembled to form one unit. The bearing ball and race are then connected to the associated bearing journal of the outer joint yoke. Finally, the inner joint yoke can be assembled with the cross member and the outer joint yoke. These units can then be connected to the guiding disc.
According to a further embodiment of the invention, the bearing race is formed as one piece and the bearing ball is pressed into the hollow-spherical bore in the bearing race. The axis of the through-bore extends perpendicular relative to the longitudinal axis of the cylindrical outer face of the bearing race. To achieve as large a joint articulation angle as possible, the bearing race is axially delimited by two end faces. The bearing race defines a longitudinal axis on which the cylindrical outer face is centered. The hollow-spherical bore is axially and eccentrically arranged between the two end faces. This embodiment is additionally advantageous since the process of fitting the bearing ball in the bearing race has been facilitated. This is due to, towards one end face, a larger aperture is obtained in the bearing race relative to the hollow-spherical bore.
The two bearing housing portions are preferably bolted to one another. Accordingly, a releasable unit is obtained which enables the exchange of components. However, it is also possible to connect the two bearing housing portions to one another after assembly, using a material-locking connection, such as a low-heat welding process. To achieve the largest possible articulation angle and to keep the amount of wear in the bearing region of the guiding disc in the guiding recess to a minimum, annular guiding plates are arranged in the annular guiding recess on both sides of the guiding disc. Also, the guiding recess is closed on the radial outside and open on the radial inside. Further, the outer diameter of the guiding plates is greater than the inner diameter of the guiding recess and smaller than the greatest diameter of the guiding recess. Furthermore, the inner diameter of the guiding plates is greater than the outer diameter of the guiding projection of the guiding disc and smaller than the outer diameter of the guiding disc.
An advantageous situation, with respect to strength, is achieved if the bridge forms an integral part of the associated outer joint yoke.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.